The secondary production of Nereis diversicolor and Scoloplos armiger (Annelida, Polychaeta) was studied at Stiffkey saltmarshes (north Norfolk coast). Production estimation on the basis of monthly sampling (August 1992–July 1993) gives 17.91 g C m−2 y−1 for N. diversicolor, 3.37 g C m−2 y−1 for S. armiger. Oxygen consumption of individuals was studied using a respirometer at four temperatures (5, 10, 15 and 20°C). At 15 °C, the relationships between O2 consumption (mg h−1) and body dry weight (mg) is Y=0.003X0.695 for S. armiger and Y=0.003X0.498 for N. diversicolor. Ammonia excretion of S. armiger tends to increase with decreasing temperature whereas it increases from 5 to 15 °C for N. diversicolor. Carbon loss through respiration for the sampling period is estimated at 32 g C m−2 y−1 for S. armiger, and 31.7 g C m−2 y−1 for N. diversicolor. About 20% of the potential supply of phytobenthic carbon in the marsh would be converted by the populations of both species. Estimations of carbon and nitrogen budgets of S. armiger are discussed.